1. Technical Field
The present invention relates to a structure of a light-emitting device utilizing a light-emitting material, such as an organic electroluminescent (EL) material.
2. Related Art
As one type of active matrix light-emitting device, a structure in which a transistor that controls a current to be supplied to a light-emitting element (such a transistor is hereinafter referred to as a “drive transistor”) is provided for each light-emitting element is known. Another type of active matrix-light emitting device is disclosed in U.S Pat. No. 6,229,506 (FIG. 2) and JP-A-2004-133240 (FIGS. 2 and 3). In this structure, a transistor that compensates for errors of the threshold voltage of a drive transistor (such a transistor is hereinafter referred to as an “initializing transistor”) is disposed between the gate electrode and the drain electrode (or source electrode) of the drive transistor. In this structure, when the initializing transistor is turned ON to allow the drive transistor to be diode-connected, the gate electrode of the drive transistor is set to be a potential corresponding to the threshold voltage. In this state, the gate electrode of the drive transistor is changed to a potential in accordance with a desired grayscale level. Then, a current which is not influenced by the threshold voltage can be supplied to the corresponding light-emitting element.
The above-described structure requires wiring patterns for electrically connecting the components related to the light emission of the light-emitting elements, for example, wiring patterns for electrically connecting the drive transistors and the initializing transistors (hereinafter such wiring patterns are referred to as “connecting portions”), and wiring patterns for electrically connecting the drive transistors and the light-emitting elements (hereinafter such wiring patterns are referred to as “electrical continuity portions”). However, if such wiring patterns are formed in different processing steps, the manufacturing process becomes complicated and the manufacturing cost is increased.
One solution to solving this problem is to form the connecting portions and the electrical continuity portions simultaneously with the formation of other components (for example, power supply lines) in the same processing step by the patterning of one conductive film. In this method, however, it is necessary to form other components, such as power supply lines, so that they can physically avoid the connecting portions and the electrical continuity portions. Because of such a restriction, for example, a sufficient width of the power supply lines cannot be ensured, and as a result, the resistance of the power supply lines cannot be sufficiently reduced.